No nest here. I've installed a couple thermostats in my house and family homes. Its fairly trivial work. Looking at the pix of the nest "wiring diagram" and

No nest here. I've installed a couple thermostats in my house and family homes. Its fairly trivial work. Looking at the pix of the nest "wiring diagram" and backplate wiring thingy, it appears to be beyond easy. (edited to add, I'm complimenting its graphical arts design or whatever, in the olden days I've actually installed thermostats that consider written docs that "the 3rd screw terminal is the W" no diagrams or writing on the device, to be adequate, the nest is much better documented and designed) The biggest "fun" you'll have is if you require lines that don't exist and have to rewire at the furnace (most commonly not having power at the thermostat) The most exciting part of thermostat installation is standards are so handy that there must be dozens of them. My advice is take a pix of the wiring before you start. No pondering what connected to what if you get confused later. This is also handy with advanced car work. In addition to the pix, draw a map of how each wire connects to what old terminal and all that. Not necessarily useful as an end product but it does kind of force the issue of studying the wiring. Also pull the wire out of the wall a little, and tape a clothes hanger or something like that to the wire. That way it can't fall into the wall, which can be quite a puzzle to solve even with the gear to fix it. Thermostat wiring is much like the old RS-232 standard in that every pin is supposed to be indestructible and can't be damaged by shorting to any other pin at any time, and of course Chinese value engineering means thats not always the case. Shutting the furnace off would probably be wise, even if in theory its impossible to damage anything by a momentary short ckt. WRT "or called a professional" note that the profit margin on sales will motivate them to not be interested in installing your thermostat, rather than installing their thermostat, and they might not sell a nest. Also a pro HVAC guy makes money installing major machinery, so unless they're hurting for work, getting a guy out there might not be easy/cheap. (edited to add I wrote from a EE perspective WRT wiring and protocols and pinouts, and one thing I overlooked is the decorative aspect of if you're changing from a giant rectangular to small round thermostat you'll have some painting, maybe even screw hole filling, maybe even hold patching to do, and frankly I donno if HVAC guys will do that kind of thing. Every job an adventure...)